In the field of optical communications, optical fiber amplifiers are used to amplify optical signals. Optical fiber amplifiers are optical amplifiers that input signal light and pumping light to optical fibers and amplify the signal light inside the optical fibers. In many cases, optical fibers used in such optical fiber amplifiers are erbium-doped optical fibers (EDFs).
A typical optical fiber used for amplification (EDF) is as long as several tens of meters. Therefore, the optical fiber is wound around a reel so as to be housed in a casing of an optical fiber amplifier (see International Publication Pamphlet No. WO2003/090325, for example). Examples of an optical fiber module in which an optical fiber is wound around a reel include a dispersion compensation fiber module in which a dispersion compensation fiber is wound around a reel (see Japanese Laid-open Patent Publication No. 2004-53733, for example).
In general, a reel around which an optical fiber is to be wound is made of metal, such as aluminum alloy, having good thermal conductivity. In many cases, such a reel is provided with an electric heater. The characteristic of an optical fiber (EDF) changes with temperature. To suppress the change in the characteristic of the optical fiber, the optical fiber is heated with the electric heater and is kept at a constant temperature (for example, 65° C.±5° C.) higher than the ambient temperature. For this reason, most reels are made of metal having good thermal conductivity.
The shapes and sizes of reels around which optical fibers are to be wound are limited by the sizes of optical fiber amplifier modules and plug-in units in which the reels are to be included. With a recent increase in the volume of optical fiber communication traffic, the degree of integration of components in optical fiber communication apparatuses is increasing so as to accommodate more modules. Under such circumstances, the sizes of optical fiber amplifier modules and plug-in units to be included in such optical fiber communication apparatuses are becoming smaller. Accordingly, the sizes of optical fiber modules in which optical fibers are wound around reels are also becoming smaller with the reels themselves becoming smaller and thinner.
Meanwhile, to realize stable optical fiber amplification, multiple-stage, for example, two-stage, optical amplification is employed in some cases. Specifically, a desired amplification factor is obtained with two optical fibers provided for first and second stages, respectively. In such a case, two optical fibers are wound around a single reel. To realize such a configuration, a space along the periphery of the reel defined by sidewalls (flanges) provided on both sides of the reel for accommodating the optical fibers needs to be divided into two spaces by a partition provided between the sidewalls. No optical fibers may be accommodated by a portion of the reel occupied by the partition. Therefore, the amount (length) of optical fibers that are wound around and accommodated by a single reel is reduced. That is, in a case where an optical fiber having a specific length is wound around and accommodated by a reel, if the reel has a partition, the size (thickness) of the reel becomes larger by an amount equal to the thickness of the partition. This is contrary to the idea of reducing the sizes of optical fiber modules.